In general, the output driver circuit of a semiconductor chip is used to output internal data through an output terminal, that is, a DQ pad, to an outside of the semiconductor chip. The output driver circuit receives the internal data and drives output data to be outputted to the DQ pad, with a preset driving strength.
FIG. 1 is a circuit diagram showing the configuration of a conventional output driver circuit, and FIG. 2 is a view showing the waveform of output data outputted to a DQ pad in the conventional output driver circuit.
Referring to FIG. 1, a conventional output driver circuit pull-up drives output data DOUT to a power supply voltage VDDQ applied from an outside, in response to a pull-up driving signal PU which is enabled to a logic low level (i.e., logic low voltage level) when internal data of a logic high level (i.e., logic high voltage level) is inputted. Also, the conventional output driver circuit pull-down drives the output data DOUT to a ground voltage applied from an outside, in response to a pull-down driving signal PD which is enabled to a logic high level when internal data of a logic low level is inputted. The output driver circuit configured in this way pull-up drives or pull-down drives the output data DOUT with a preset driving strength.
However, in the case where the level of the power supply voltage VDDQ supplied to the output driver circuit varies, the driving strength for pull-up driving or pull-down driving the output data DOUT changes, and accordingly, as shown in FIG. 2, the slew rate of the output data DOUT changes (as indicated by the arrows and the dotted lines). That is to say, the output characteristic of the output data DOUT outputted from the conventional output driver circuit may be degraded due to the change in the slew rate according to the level of the power supply voltage VDDQ.